(If desired, use a cake leveler or large serrated knife to slice cake into 2 or 3 layers to fill with frosting. I didn’t bother with that step this time around).
Place a smear of frosting on a plate or cake circle (to keep the cake from sliding while you decorate it) and center cake on the circle. Spread a layer of gray frosting over the cake and smooth with an offset spatula and acetate. (You’ll need to be able to punch into this layer to make the ‘holes’ in the top frosting layer, so I put it on fairly thick – thicker than a crumb coat.) Freeze for 10 minutes.
Add a yellow layer of frosting over the gray frosting and smooth with an offset spatula and acetate.
(This will be the most time-consuming step-) Make the pickleball cut-outs! With the back of a small piping tip, press and rotate the tip through the green frosting layer into the gray one. (Don’t go all the way through the gray one.) As you rotate the tip back out, it should pull the green frosting away, leaving a gray base to the cut-out.
Wipe the frosting out of the tip, and repeat! If you're having any trouble at this step - first, make sure you twist/rotate the tip out of the frosting. Pulling it straight out will usually just leave the frosting in the base of the cut-out. Next, I found a metal piping tip worked better than a plastic one. You can try heating it or wetting it if just the oil isn't working well enough. Chilling the cake may also help.
(More details in the post intro if you're having trouble - and please leave a comment or shoot me an email if you’re still having trouble.)
Transfer green frosting to a piping bag fitted with a grass tip, and pipe a rim of grass around the cake base. High-five yourself on your awesome cake - and enjoy!